Methacrylic acid esters are primarily used as raw material in acrylic resins, while there is great demand for use as comonomers in applications such as paints, adhesives, and resin modifiers. Some known examples in industrial manufacturing methods are ACH (acetone cyanohydrin) methods using acetone and hydrogen cyanide as raw materials, and methods for direct oxidation using isobutylene and tert-butyl alcohol as raw materials. Those chemical production methods depend on fossil raw materials and require a great deal of energy.
In recent years, technologies for producing various chemicals from biomass as a carbon source substituting conventional fossil raw materials have attracted attention from the viewpoints of environmental protection and prevention of global warming. Although methacrylic acid esters are also expected to be produced from biomass raw materials, a specific production example from biomass raw materials using a biocatalyst has not been reported.
For example, methods using microorganisms existing in nature to produce 2-hydroxyisobutyric acid and 3-hydroxyisobutyric acid as precursors of methacrylic acid from a natural source such as sugar have been proposed (refer to Patent Literatures 1 and 2, and Non-Patent Literature 1). However, in those methods, the procedures for dehydrating precursors and forming methacrylic acid still depend on chemical techniques.
In addition, methods for forming methacrylic acid from glucose using recombinant microorganisms that do not exist naturally and are produced by introducing multiple enzyme genes have been proposed; however, those methods are results of combining an already known enzyme reaction and a hypothetical enzyme reaction analogized from such reaction, and thus have not been proven (refer to Patent Literatures 3 to 5) In particular, although Patent Literature 5 shows examples of various biocatalysts (hydrolase, wax ester synthetase, alcohol acetyltransferase) having common ester formation activity, it is unclear whether the exemplified biocatalysts have the synthetic activity for methacrylic acid ester.
Furthermore, Patent Literature 6 discloses a method for producing acrylic acid esters through reaction of hydrolase in the presence of acrylyl-CoA and alcohol. The same document suggests that methacrylic acid esters are also produced by such a method. However, when taking account of diversity and substrate specificity of biocatalysts, it merely suggests production of acrylic acid esters by a certain type of hydrolase, and it is unclear whether the hydrolase is capable of producing methacrylic acid esters having different structures. Furthermore, it is totally unclear whether other types of biocatalysts having different reaction mechanisms are capable of producing methacrylic acid esters. In addition, when esters are synthesized by the hydrolase described in Patent Literature 6, it is assumed that the formed ester will be decomposed by the hydrolysis activity in the first place, and thus such a production method is quite unlikely to be effective.
On the other hand, alcohol acetyltransferase has been known as a fruity flavor synthetase. Patent Literature 7 identifies the same enzyme genes contained in specific fruits and proposes synthetic methods of various esters that are of fruit flavors. However, whether methacrylic acid esters are synthesizable with those enzymes is not reported and has been completely unclear.
As stated above, although some proposals or studies have been made, there are no examples of methacrylic acid esters actually produced through enzymatic reactions, and thus the establishment of an effective production method has been desired.